Every so often, Facebook does something that sets off the alarm of privacy advocates—perhaps it's inevitable when you're the largest social network on the planet with over 1.65 billion users. Right now that something is tapping into your smartphone's location data to suggest friends based on where you're at or where you've been.

Why is this unsettling? Getting past the theoretical situations and jumping straight into a real-world example that's a bit creepy on Facebook's part, Kashmir Hill at Fusion writes an anecdotal account of a man on Facebook who suspected it had tracked his location to figure out who he was meeting with. The man was a parent who recently attended a support group for suicidal teens.

"The next morning, he told me, he opened Facebook to find that one of the anonymous parents at the gathering popped up as a 'person you may know.' The two parents hadn't exchanged contact information," Hill writes.

The only connection between the two people was having been at the same place at the same time with their smartphones turned on. When the man checked his privacy settings, sure enough Facebook was set to "always" have access to location.

His suspicions about location tracking weren't paranoia.

"People You May Know are people on Facebook that you might know," a spokesperson for Facebook said. "We show you people based on mutual friends, work and education information, networks you're part of, contacts you've imported, and many other factors."

The spokesperson went on to add that location information alone isn't enough to indicate that two people might be friends, which is why "location is only one of the factors we use to suggest people you may know."

There are situations where friend requests based on location data might come in handy, such as a high school reunion or some other social gathering where you're likely to have some sort of connection. But there are also situations where it's entirely inappropriate, including anonymous group sessions.

If you're not comfortable with getting or being part of Facebook's friend requests based on location tracking, you can turn the feature off in your phone's Privacy settings.